Since the introduction of OS X Lion, the Mac has had new options for adjusting the dimensions of windows. Before Lion, you were limited to clicking and dragging a window's bottom right corner to adjust its size, or using the green and yellow buttons in the window's upper left corner to set the window to predefined sizes.
Screen shot courtesy of Coyote Moon, Inc.
With Lion and later versions of the OS, you have a great deal more flexibility, including some secret methods of setting window size using the option key.
Oops. I guess it's not a secret anymore. If you want to learn the myriad ways of resizing your Mac's windows, take a look at: